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From: Namjae Jeon <linkinjeon@gmail.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: "Namjae Jeon" <namjae.jeon@samsung.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Linux FS-devel Mailing List" <linux-fsdevel@vger.kernel.org>,
	gregkh <gregkh@linuxfoundation.org>,
	"Valdis Kletnieks" <valdis.kletnieks@vt.edu>,
	"Christoph Hellwig" <hch@lst.de>,
	sj1557.seo@samsung.com, "Pali Rohár" <pali.rohar@gmail.com>
Subject: Re: [PATCH v10 09/14] exfat: add misc operations
Date: Wed, 15 Jan 2020 22:30:59 +0900
Message-ID: <CAKYAXd9_qmanQCcrdpScFWvPXuZvk4jhv7Gc=t_vRL9zqWNSjA@mail.gmail.com> (raw)
In-Reply-To: <CAK8P3a3Vqz=T_=sFwBBPa2_Hi_dA=BwWod=L9JkLxUgi=aKNWw@mail.gmail.com>

2020-01-15 19:10 GMT+09:00, Arnd Bergmann <arnd@arndb.de>:
> On Wed, Jan 15, 2020 at 9:28 AM Namjae Jeon <namjae.jeon@samsung.com>
> wrote:
>
>> +#define SECS_PER_MIN    (60)
>> +#define TIMEZONE_SEC(x)        ((x) * 15 * SECS_PER_MIN)
>> +
>> +static void exfat_adjust_tz(struct timespec64 *ts, u8 tz_off)
>> +{
>> +       if (tz_off <= 0x3F)
>> +               ts->tv_sec -= TIMEZONE_SEC(tz_off);
>> +       else /* 0x40 <= (tz_off & 0x7F) <=0x7F */
>> +               ts->tv_sec += TIMEZONE_SEC(0x80 - tz_off);
>> +}
>> +
>> +static inline int exfat_tz_offset(struct exfat_sb_info *sbi)
>> +{
>> +       if (sbi->options.time_offset)
>> +               return sbi->options.time_offset;
>> +       return sys_tz.tz_minuteswest;
>> +}
>> +
>> +/* Convert a EXFAT time/date pair to a UNIX date (seconds since 1 1 70).
>> */
>> +void exfat_get_entry_time(struct exfat_sb_info *sbi, struct timespec64
>> *ts,
>> +               __le16 time, __le16 date, u8 tz)
>> +{
>> +       u16 t = le16_to_cpu(time);
>> +       u16 d = le16_to_cpu(date);
>> +
>> +       ts->tv_sec = mktime64(1980 + (d >> 9), d >> 5 & 0x000F, d &
>> 0x001F,
>> +                             t >> 11, (t >> 5) & 0x003F, (t & 0x001F) <<
>> 1);
>> +       ts->tv_nsec = 0;
>
> This part looks good to me now.
Thanks.
>
>> +       if (tz & EXFAT_TZ_VALID)
>> +               /* Treat as UTC time, but need to adjust timezone to UTC0
>> */
>> +               exfat_adjust_tz(ts, tz & ~EXFAT_TZ_VALID);
>> +       else
>> +               /* Treat as local time */
>> +               ts->tv_sec -= exfat_tz_offset(sbi) * SECS_PER_MIN;
>> +}
>
> Whereas this seems rather complex, when it deals with three different
> cases:
>
> - timezone stored in inode
> - timezone offset passed as mount option
> - local time from sys_tz.tz_minuteswest
>
> Does the exfat specification require to use some notion of 'local time'
> here
> as the fallback? The problem with sys_tz.tz_minuteswest is that it is
> not too well-defined,
It is not described in the specification. I don't know exactly what
the problem is because sys_tz.tz_minuteswest seems to work fine to me.
It can be random garbage value ?
> so if there is a choice, falling back to UTC would
> be nicer.
Okay.
>
>> +/* Convert linear UNIX date to a EXFAT time/date pair. */
>> +void exfat_set_entry_time(struct exfat_sb_info *sbi, struct timespec64
>> *ts,
>> +               __le16 *time, __le16 *date, u8 *tz)
>> +{
>> +       struct tm tm;
>> +       u16 t, d;
>> +
>> +       /* clamp to the range valid in the exfat on-disk representation.
>> */
>> +       time64_to_tm(clamp_t(time64_t, ts->tv_sec,
>> EXFAT_MIN_TIMESTAMP_SECS,
>> +               EXFAT_MAX_TIMESTAMP_SECS), -exfat_tz_offset(sbi) *
>> SECS_PER_MIN,
>> +               &tm);
>
> I think you can drop the clamping here, as thes_time_min/s_time_max fields
> should take care of that.
Okay.
>
> For writing out timestamps, it may be best to always encode them as UTC
> and set set timezone-valid bit for that. That way, the min/max values
> are known at compile time regardless of which time zone the machine
> thinks it is in.
Okay, I will check it.
Thanks for your review!
>
>       Arnd
>

  reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200115082818epcas1p4892a99345626188afd111ee263132458@epcas1p4.samsung.com>
2020-01-15  8:24 ` [PATCH v10 00/14] add the latest exfat driver Namjae Jeon
     [not found]   ` <CGME20200115082819epcas1p3303009557f8bf670b47991530f380ef7@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 01/14] exfat: add in-memory and on-disk structures and headers Namjae Jeon
     [not found]   ` <CGME20200115082819epcas1p3825d5bed592a8378ad26254d07d59b18@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 02/14] exfat: add super block operations Namjae Jeon
     [not found]   ` <CGME20200115082820epcas1p34ebebebaf610fd61c4e9882fca8ddbd5@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 03/14] exfat: add inode operations Namjae Jeon
2020-01-15 10:25       ` Arnd Bergmann
2020-01-15 13:39         ` Namjae Jeon
2020-01-17  9:25       ` Pali Rohár
2020-01-17 11:17       ` Pali Rohár
     [not found]   ` <CGME20200115082821epcas1p3db1f70cf53185c40934c3a754c65e648@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 04/14] exfat: add directory operations Namjae Jeon
2020-01-17 11:13       ` Pali Rohár
     [not found]   ` <CGME20200115082821epcas1p4d76d8668dfac70ae3e3889d4ccb6c3ee@epcas1p4.samsung.com>
2020-01-15  8:24     ` [PATCH v10 05/14] exfat: add file operations Namjae Jeon
2020-01-15  9:56       ` Arnd Bergmann
2020-01-15 13:07         ` Namjae Jeon
2020-01-17  9:18       ` Pali Rohár
2020-01-17 12:12         ` Namjae Jeon
     [not found]   ` <CGME20200115082822epcas1p37aca37dad0aa9159d7eddde01edfeec2@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 06/14] exfat: add fat entry operations Namjae Jeon
     [not found]   ` <CGME20200115082822epcas1p384d080724d8bb0a8cd4c3e3015a0895c@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 07/14] exfat: add bitmap operations Namjae Jeon
     [not found]   ` <CGME20200115082823epcas1p27ec5ff6d384f148d826529f573173b04@epcas1p2.samsung.com>
2020-01-15  8:24     ` [PATCH v10 08/14] exfat: add exfat cache Namjae Jeon
     [not found]   ` <CGME20200115082824epcas1p4eb45d088c2f88149acb94563c4a9b276@epcas1p4.samsung.com>
2020-01-15  8:24     ` [PATCH v10 09/14] exfat: add misc operations Namjae Jeon
2020-01-15 10:10       ` Arnd Bergmann
2020-01-15 13:30         ` Namjae Jeon [this message]
2020-01-15 13:38           ` Pali Rohár
2020-01-15 13:50             ` Arnd Bergmann
2020-01-15 14:24               ` Pali Rohár
2020-01-15 15:03                 ` Arnd Bergmann
2020-01-15 15:39                   ` Pali Rohár
2020-01-15 15:52                     ` Arnd Bergmann
2020-01-16 10:19                       ` Pali Rohár
2020-01-16 10:23                         ` Christoph Hellwig
2020-01-16 16:00                           ` Pali Rohár
2020-01-17  2:59                       ` Namjae Jeon
2020-01-17 10:13                         ` Arnd Bergmann
2020-01-17 12:13                           ` Namjae Jeon
     [not found]   ` <CGME20200115082824epcas1p23a0fa255a5833c6dcd2479b384f37740@epcas1p2.samsung.com>
2020-01-15  8:24     ` [PATCH v10 10/14] exfat: add nls operations Namjae Jeon
     [not found]   ` <CGME20200115082825epcas1p1f22ddca6dbf5d70e65d3b0e3c25c3a59@epcas1p1.samsung.com>
2020-01-15  8:24     ` [PATCH v10 11/14] exfat: add Kconfig and Makefile Namjae Jeon
2020-01-15  9:39       ` Pali Rohár
2020-01-17  4:22         ` Namjae Jeon
2020-01-17  9:12           ` Pali Rohár
2020-01-17 11:59             ` Namjae Jeon
     [not found]   ` <CGME20200115082825epcas1p4a0d63d53d8737a84fe8867bc1e63811e@epcas1p4.samsung.com>
2020-01-15  8:24     ` [PATCH v10 12/14] exfat: add exfat in fs/Kconfig and fs/Makefile Namjae Jeon
     [not found]   ` <CGME20200115082826epcas1p117191a39ecccaef5a9b5cbe77b05c5a5@epcas1p1.samsung.com>
2020-01-15  8:24     ` [PATCH v10 13/14] MAINTAINERS: add exfat filesystem Namjae Jeon
     [not found]   ` <CGME20200115082826epcas1p3475ce2b4d03234dc96ced428be582eb3@epcas1p3.samsung.com>
2020-01-15  8:24     ` [PATCH v10 14/14] staging: exfat: make staging/exfat and fs/exfat mutually exclusive Namjae Jeon
2020-01-15  8:56       ` Greg KH
2020-01-15 13:06         ` Namjae Jeon
2020-01-15  9:47   ` [PATCH v10 00/14] add the latest exfat driver Pali Rohár
2020-01-15 13:05     ` Namjae Jeon
2020-01-16 10:51     ` Christoph Hellwig
2020-01-16 11:32       ` Pali Rohár
2020-01-16 13:01       ` Greg KH

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